Tapped potentiometer circuit



Jul 18, 1961 F. R. BRADLEY, JR

TAPPED POTENTIOMETER CIRCUIT Filed June 17, 1958 FIG. 2

FIG. 6

INVENTOR FRANK R. BRADLEY JR BY I ATTORNEYS United States Patent 2,993,185 TAPPED POTENTIONIETER CIRCUIT Frank R. Bradley, Jr., 215 W. 88th St., New York, N.Y. Filed June 17, 1958, Ser. No. 742,627 2 Claims. (Cl. 338176) This invention relates to the art of potentiometer circuits and more particularly to a tapped potentiometer.

As conducive to an understanding of the invention, it is noted that where, for example, a potentiometer has a plus and minus applied potential between its ends and is tapped to establish a precise zero reference point with respect to the applied potential or where the potentiometer is tapped between its ends to lower the impedance presented by the potentiometer, and the tap is held at a fixed potential such as ground; due to the physical dimension of the wiper, from the position that the leading edge of the wiper comes to the region of the tap, to the position that the trailing edge of the wiper leaves the region of the tap, it will short out a significant fraction of the resistance element of the potentiometer and the resultant output voltage will have a region of reduced voltage gradient as a function of wiper position.

Where such region of reduced voltage gradient causes a displacement of the curve of the output voltage, errors will be caused in the system in which the potentiometer is used with resultant malfunctioning of such system.

It is accordingly among the objects of the invention to provide a tapped potentiometer circuit which is relatively simple in construction and which although there is still a region of reduced voltage gradient at either or both ends of the region of the tap, will provide an increased voltage step that will prevent any displacement of the curve of the output voltage due to such region of reduced voltage gradient.

According to the invention, these objects are accomplished by the arrangement and combination of elements hereinafter described and particularly recited in the claims.

In the accompanying drawings in which are shown one or more of various possible embodiments of the several features of the invention,

FIG. 1 is a circuit diagram of a tapped potentiometer circuit according to the invention,

FIG. 2 is a diagrammatic view illustrating the displacement of the curve of the output voltage of a conventional tapped potentiometer.

FIG. 3 is a view similar to FIG. 2 of the curve of the output voltage of a potentiometer circuit according to the invention,

FIGS. 4, 5 and 6 are fragmentary detail views on a greatly enlarged scale of tapped otentiometers according to various embodiments of the invention.

Referring now to FIG. 1 of the drawings, in the illustrative embodiment shown, the potentiometer 11 is of the wire wound type having terminals 12 and 13 at its respective ends which may be connected to sources of potential E1 and E2. The potentiometer winding is split as at 14 as shown in enlarged scale in FIG. 4 and a length of resistance wire 15 of value equal to that which would normally be sorted out by the wiper 16 is connected between the ends 17, 18 of the split portion of the main potentiometer winding, and such wire 15 is illustratively connected to ground. As shown in FIG. 4, the width of the wiper 16 is such that it illustratively engages two of the turns T of the potentiometer winding.

For use in the normal circuits in which such tapped potentiometersare employed, the fol-lowing relationship is preferably established:

ails

where E1 and E2 are the voltages applied to terminals 12 and 13 and R1 and R2 are the portions of the main potentiometer winding on each side of the tap.

With this relationship, most of the current flows through the windings R1 and R2 and only a small dilierential current flows through the wire 15 to ground.

With the conventional tapped potentiometer there is a region of reduced voltage gradient as shown at 21 in FIG. 2 which causes a dead spot in the output curve. This results in a displacement of the curve as is shown in FIG. 2 in the output voltage due to the fact that the wiper of the potentiometer shorts several turns of the wire in a wire wound potentiometer.

With the circuit shown in FIGS. 1 and 4, for example, due to the added resistance of wire 15, although there is a region of reduced voltage gradient as shown in FIG. 3 at 22, there will be an increased voltage step 23 which will cause the resultant curve on both sides of the tap to be co-linear. As a result, errors in the equipment in which the tapped potentiometer according to the invention is employed will be greatly minimized.

In the embodiment shown in FIG. 5 instead of splitting the winding of the potentiometer, one complete winding turn is eliminated and a length of wire 15 of the desired value is connected between the ends 17, 18 of the severed potentiometer winding.

In the embodiment shown in FIG. 6, a film type potentiometer is shown and the film 24 is broken at 14' and a resistor 26 connected to the ends 17" and 18" of such film.

As the embodiments shown in FIGS. 5 and 6 function in the identical manner to that shown in FIGS. 1 and 4, no further description thereof will be made.

As many changes could be made in the above system and equipment, and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. A potentiometer having a main resistance element of the film type interrupted between its ends, a wiper arm adapted to engage said resistance element, an additional resistance element electrically connected across the interrupted portion of the main resistance element and a tap connected to said additional resistance element.

2. The combination set forth in claim 1 in which said film is broken between its ends to define a gap, and said additional resistance element is a resistor connected across said gap.

References Cited in the file of this patent UNITED STATES PATENTS 2,103,873 Severin et a1 Dec. 28, 1937 2,662,144 Wilentchik Dec. 8, 1953 2,729,727 Molloy et a1. Jan. 3, 1956 

